Measuring the angular diameter of celestial bodies has long been the main purpose of stellar interferometry and was its historical motivation. Nowadays, stellar interferometry is widely used for various ... [more ▼]

Measuring the angular diameter of celestial bodies has long been the main purpose of stellar interferometry and was its historical motivation. Nowadays, stellar interferometry is widely used for various other scientific purposes that require very high angular resolution measurements. In terms of angular spatial scales probed, o [less ▲]

The asteroids were observed photometrically during the 1980 and 1981 oppositions, respectively. The V lightcurve of 86 Semele displays two asymmetric maxima and minima with a total amplitude DeltaV = 0.18 ... [more ▼]

Spectral variations detected within the last three decades for He II 4686 A, forbidden lines O III and other high excitation lines in the low-excitation planetary nebula HD 138403, are shown to suggest ... [more ▼]

Spectral variations detected within the last three decades for He II 4686 A, forbidden lines O III and other high excitation lines in the low-excitation planetary nebula HD 138403, are shown to suggest appreciable activity in the deep atmospheric layers of the nucleus, and an increase of the excitation of the nebula. The spectrum of the nebula is found to be unusual due to the presence of red and blue emission satellites around the central Balmer (H-beta - H9) lines and forbidden lines O II 3726, 3729 A, with a velocity separation equal to plus 122 and minus 126 km/s, respectively. These features are interpreted as evidence for mass outflow from the central object via the selective radiation process of edge and/or line locking mechanisms. [less ▲]

Direct plates in narrow bands (H , [0 NI], [S Ii]) and in the broad (B)-band show that the nebula surrounding the nova- like object HD 87643 is of reflective origin. Furthermore, a spectrogram of the ... [more ▼]

Direct plates in narrow bands (H , [0 NI], [S Ii]) and in the broad (B)-band show that the nebula surrounding the nova- like object HD 87643 is of reflective origin. Furthermore, a spectrogram of the filamentary condensation lying east-west at 17" north of HD 87643 reveals strong Balmer emission lines, with a P Cygni structure at H fl H e, as well as many diffuse emission lines of Fe II: such features essentially form a replica of the spectrum of the central object. These results and other arguments strongly support the idea that the reflection nebula surrounding HD 87643 is associated with the mass-outflow observed from the central hot star. Key words: reflection nebula - HD 87643 - mass-loss [less ▲]

The two fast-moving asteroids 1978 CA and 1978 DA, discovered in February 1978 with the ESO Schmidt telescope at La Silla (Chile), were observed with a photoelectric photometer attached to the 1-m ESO ... [more ▼]

The two fast-moving asteroids 1978 CA and 1978 DA, discovered in February 1978 with the ESO Schmidt telescope at La Silla (Chile), were observed with a photoelectric photometer attached to the 1-m ESO telescope. The light curve of 1978 CA displays two fairly symmetric maxima and minima with a total amplitude of 0.8 mag in V. The synodic period of rotation found is 3 h 45 m and places 1978 CA as the third fastest rotator among all known solar objects. Concerning the minor planet 1978 DA, light variations covering one full cycle of rotation could not be monitored. Nevertheless, the rotation period exceeds 5 h, and the total amplitude is greater than 0.35 mag. [less ▲]

UBV photometric observations of the earth-crossing asteroid 1978 CA and the Mars-crosser 1978 DA are reported. Light curves are plotted which indicate that 1978 CA has a rotation period of approximately 3 ... [more ▼]

UBV photometric observations of the earth-crossing asteroid 1978 CA and the Mars-crosser 1978 DA are reported. Light curves are plotted which indicate that 1978 CA has a rotation period of approximately 3 hr 45 min and that 1978 DA rotates about its axis much more slowly than 1978 CA. The following color indices are determined: (B-V) of approximately 0.90 and (U-B) of about 0.48 for 1978 CA and (B-V) = 0.83 and (U-B) = 0.41 for 1978 DA. A model that may explain the observed smooth and nearly symmetric light curve of 1978 CA is briefly discussed. [less ▲]

A triaxial-ellipsoid model is used to simulate the smooth and nearly symmetric light curves that are usually characteristic of asteroids which exhibit large brightness variations. The mathematical model ... [more ▼]

A triaxial-ellipsoid model is used to simulate the smooth and nearly symmetric light curves that are usually characteristic of asteroids which exhibit large brightness variations. The mathematical model is developed and applied to two problems involving an asteroid moving with its rotational axis either perpendicular to or lying within the plane containing the sun and earth. The numerical results obtained are compared with Dunlap's (1971) simulations of asteroid brightness variations, and it is argued that typical asteroid phase coefficients cannot be interpreted unambiguously. The results are shown to favor the Hapke-Irvine relation for describing the scattering properties of a dark asteroid surface. [less ▲]

The results are presented of photographic observations of asteroid positions made in August 1976 at La Silla, Chile. The quality of the sky characteristics made it possible to record objects with the ... [more ▼]

The results are presented of photographic observations of asteroid positions made in August 1976 at La Silla, Chile. The quality of the sky characteristics made it possible to record objects with the magnitude 17. Measurements of all plates were conducted with the aid of the Ascorecord measuring machine of the Royal Belgian Observatory. The reduction method employed is based on the use of five reference stars. The equatorial planet coordinates can be easily obtained from the employed parameters with the aid of the formulas considered by Smart (1944). In the evaluation procedures use was made of the SAO catalog which had been recorded on magnetic tape by the Strasbourg Observatory. Three new asteroids were discovered. The obtained data are presented in two tables. [less ▲]